Land mobile radio (LMR) systems are typically narrowband communications systems used by public safety agencies, for example, emergency first responder organizations, such as police or fire departments, or public works organizations. Users (also referred to as subscribers) on LMR systems may communicate via mobile or portable user terminals, and portable radios or radios in vehicles.
A portion of the United States broadband spectrum, i.e., the 700 MHz spectrum, additionally has been allocated for public safety use, wherein all public safety agencies and all applications used by these public safety agencies are expected to share this portion of the broadband spectrum. Long Term Evolution (LTE) has been selected as the air interface technology for this 700 MHz spectrum. In addition to public safety devices, user equipment (UE) operated by secondary users (for example, utility or government workers) and/or commercial users also may share this portion of the broadband spectrum. Throughout the world, public safety has opportunities to share radio spectrum with secondary and commercial users. This creates a challenge in determining the appropriate priority for a UE operating on the shared broadband spectrum. For example, if a UE operated by a police officer and a UE operated by a commercial user contend for the same resources, a determination must be made as to which user equipment is given access to those resources.
LTE is a broadband standard for wireless data communications. A 3GPP (Third Generation Partnership Project) LTE system includes, among other components, a core network for handling data traffic and a network of eNodeBs (eNBs), each of which functions as a base station for the LTE system and forwards user data and signaling between the core network and UEs operating on the LTE system. In a 3GPP LTE system, in order to control access to the network by a UE, and in particular to a Random Access Channel (RACH), various barring capabilities have been defined which are intended to limit surges is usage of the RACH. These barring capabilities include, but are not limited to Access Class Barring, Service-Specific Access Control, Extended Access Barring, and Closed Subscriber Group checking.
An eNodeB may be configured to limit user access by broadcasting various parameters associated with the barring capabilities, such as access class barring (ACB) parameters, in a downlink SIB2 (System Information Block Type 2) message. UEs are pre-configured with at least one access class (AC) in a SIM (subscriber identity module) and use the access class(es) to determine whether they can access the system, that is, begin to utilize an access channel, based on the SIB2 message and their stored AC(es). For example, commercial users may be randomly assigned an AC of ‘0’ to ‘9,’ AC ‘10’ is reserved for E911 calls, ACs ‘11’ and ‘15’ are reserved for network administrative device, and the remaining ACs of ‘12’ to ‘14’ are reserved for public safety and next generation network (NGN) government emergency telecommunications service (GETS) workers, that is, AC ‘12’ is reserved for security services (for example, police), AC ‘13’ is reserved for public utilities, and AC ‘14’ is reserved for emergency services (that is, emergency responders, such as fire and emergency medical personnel (EMTs)).
The ACB parameters transmitted by the eNodeB over-the-air include ‘ac-BarringFactor,’ ac-BarringTime, ‘ac_BarringForEmergencyFactor,’ and ‘ac-BarringForSpecialAC.’ For users with an AC of 0-9, the user's UE generates a random number (‘RAND’) and compares the RAND to a threshold value (the ac-BarringFactor received from the eNodeB over-the-air). If the RAND is less than the threshold, then the UE can access the network. Otherwise the UE has to wait. Thus, by setting an ac-BarringFactor, an eNodeB can control UE access and mitigate congestion. If the user is making an emergency call (AC 10), then their access is controlled by an ac_BarringForEmergencyFactor parameter, and for users having an AC of 11-15, their access is controlled by the parameter ac-BarringForSpecialAC. If a UE utilizes AC 10 (that is, dials an emergency number) or is configured with AC 10-15, and the corresponding eNodeB parameter indicates barring should not take place, the UE can immediately access the eNodeB's RACH.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.